The cornea of the eye plays a role in focusing light. By changing the shape of the cornea, it is possible to correct a patient's vision. Common surgical procedures for changing the shape of the cornea include temporarily removing the epithelium of the cornea to expose the underlying stroma, ablating selected portions of the stroma with a laser, and replacing the epithelium over the stroma. Two known surgical methods are LASEK (“Laser assisted Sub Epithelial Keratomilieusis”) and LASIK (“Laser assisted In situ Keratomilieusis”) surgery.
In LASEK surgery, an incision along a circular arc on the cornea is made and the resulting flap is pulled back to expose the stroma of the cornea. The flap includes the epithelium and the Bowman's membrane separating the epithelium from the stroma. Unlike the flap that is made during LASIK, this flap does not include any portion of the stroma. Thus, when the flap is pulled back, it is the surface of the stroma, and not the interior of the stroma, that is exposed to the laser. This procedure thus results in a lower risk of complications.
In practice, because the epithelium is so thin, it is difficult to cut a flap without cutting into the stroma. It is known, however, that bathing the cornea in a solution of alcohol and water causes separation of epithelial cells from the stroma. Once the epithelium is separated from the stroma, cutting the flap becomes easier.
A difficulty with the use of the foregoing solution is that alcohol is toxic to cells. Thus, if the concentration of alcohol is excessive, or if the solution is left on the cornea for too long, a significant number of epithelial cells will die. If this occurs, the flap will not re-attach itself effectively to the stroma.